1. Field of the Invention
The present invention relates to a lead material for ceramic package ICs. More particularly, it relates to a lead material for the side-brazed leadframe of dual-in-line ceramic package and for the lead wire of pin-grid array IC. The lead material is made into input/output terminals after brazing with heating at 800.degree. to 900.degree. C. After brazing, it has a Vickers' hardness of at least 130.
2. Discussion of the Background
Usually, the substrate of side-brazed ICs is made of ceramics and the metallized parts on both sides of the substrate are connected to the leadframe as the terminals by silver soldering.
The material of the leadframe is the Fe-42Ni alloy (F-30 alloy of ASTM Standards). This alloy is used because it has a coefficient of thermal expansion close to that of ceramics and it does not apply strain to (and hence does not cause damage to) the ceramic substrate during the cooling process after silver soldering at 800.degree. to 900.degree. C. This F-30 alloy has an advantage that it has a Vickers' hardness higher than 130 even after brazing at 800.degree. to 900.degree. C.
On the other hand, this F-30 alloy has a disadvantage of its low electric conductivity, i.e., 3% IACS. Accordingly, it has a low thermal conductivity and is liable to generate Joule heat when used as a lead material for ICs and is poor in dissipation of heat generated in the IC elements.
There has been a demand for a new material to replace the F-30 alloy poor in heat dissipation, because recent ICs generate more heat than before as the density of elements increases.
A material that meets this requirement is a copper alloy. However, it has a serious drawback in that it softens and loses its strength as the result of heating for silver soldering at 800.degree. to 900.degree. C. In addition, a copper alloy superior in strength and heat resistance has a low conductivity as with F-30 alloy.
In the case of pin-grid array IC, the headed wire and the metallized electrode are connected together by silver soldering at 800.degree. to 900.degree. C. as in the case of side-brazed IC. Except that the leadframe for side-brazing is made of strip, both the leadframe and the wire receive the same strain due to cooling after brazing. The lead made of F-30 alloy now in use for pin-grid array ICs is poor in heat dissipation as mentioned above, and there has been a demand for a new material to replace it.
The present invention was made to overcome the disadvantages of F-30 alloy or a copper alloy as a substitute of F-30 alloy which has been used as a lead material for ceramic package ICs, e.g., side-brazed ICs of dual-in-line type ceramic package and pin-grid array ICs.